VIBRATION AT HIGHWAY SPEED

SAAB Other

I have a Saab 9-5 wagon, 2004, 36K mileage, 2.3 engine. At highway speeds (65 mph and above), I get a noticeable and unpleasant vibration in the steering wheel and through the floor boards, also noticed by front and rear passengers. Had tires balanced 2X, wheels aligned, 2 rims repaired and 2 rims replaced. Problem still exists. I notice some people with a similar problem used road force tire balancing, which proved successful. What do you recommend?
Thanks.